Not exactly, it is more like, not brilliant. It doesn't really mean the subject is necessarily incapable or incompetent, just not superlative, not spectacular in the eyes of the commenter, at that moment. If someone said this, they just might have to take it back later, and 'eat crow'. What it really tells us is that the commenter is sarcastic.

The meaning is a little loose though, it could be said about someone that is a complete incompetent, a ne'er do well, a good for nothing.